1. Field of the Invention
The invention is concerned with ion beam adjustment, and directed particularly to adjust the ion beam between a mass analyzer and a workpiece by using one or more specific shaped magnetic fields.
2. Description of Related Art
Ion implantation is a ballistic process used to introduce into a substrate with ions, atoms or molecules, generally referred to as dopants, to make materials with useful properties. Of particular interest, ion implantation is a common process used in making modem integrated circuits. Ion implantation may also be used for other purpose, like thin film deposition or formation with controlled thickness and predefined surface properties for manufacturing optical display devices such as flat panel displays.
In general, an ion implanter has at least an ion source, a mass analyzer and a substrate holder. The ion source is used to ionize one or more material to generate numerous ions, and the mass analyzer is used to filter these ions so that the selected ion beam has only substantially ions with desired specific mass-to-charge ratio. Then, the workpiece held by the substrate holder is implanted by the selected ion beam. Herein, the workpiece can be a semiconductor substrate, a glass plate or other bulk materials.
In general, without further focusing or adjusting, the ion beam just exited from the mass analyzer would not have a desired shape and property other than corrected beam current and energy. For example, the cross-sectional shape of ion beam may be irregular, and the ion beam current distribution on the cross section may be non-uniform or far away from Gaussian distribution. Moreover, different implantations applications may prefer different ion beams with different shapes. For example, a narrower ion beam may be beneficial than a wider ion beam for implanting a region with more defined boundary on a workpiece. Accordingly, the ion implanter usually has one or more control assemblies which are capable of applying the magnetic field or the electromagnetic field on the ion beam in a region between the mass analyzer and the substrate holder. The trajectory of each charged particle, such as ion, in the ion beam will be affected by the applied magnetic/electromagnetic field, and then the properties of ion beam may be adjusted. For example, a diverse ion beam may be collimated, a ribbon shape ion beam may be focused to form a spot beam at the surface of the workpiece, and the ion beam current density distribution may be modified to become Gaussian-like distribution with beam width and height in the preferred rang by controlling the ion beam envelope.
There is a number of conventional control assemblies used in ion implanter. For example, as shown in FIG. 1A, one popular conventional control assembly has two mutual parallel straight bar magnets 11/12 having the coils 13 uniformly disposed on the straight support rods 14. Hence, by adjusting separately the electrical current directions through the coils 13, different magnet fields may elongate or compress the ion beam 15 (direction into the paper and vertical to the two straight bar magnets 11/12) when the ion beam is directed through a space between the straight bar magnets 11/12. Another conventional control assembly, as shown in FIG. 1B, is similar with the above except that the coils 13 are non-uniformly disposed on the straight support rods 14. Still another conventional control assembly, as shown in FIG. 1C, is similar with the above except that one additional straight bar magnet 16 is configured to mechanically connect the two straight bar magnets 11/12 for forming a U-shape magnet structure. Herein, the coils 13 may be uniformly or non-uniformly disposed on the additional straight bar magnet 16. One more conventional control assembly, as shown in FIG. 1D, is similar with the above except that two additional straight bar magnets 16/17 are configured to mechanically connect the two straight bar magnets 11/12 for forming a rectangle magnet structure. Herein, the coils 13 may be uniformly or non-uniformly disposed on the two additional straight bar magnets 16/17. Moreover, one or more electric element 18 may be disposed on one or two additional straight bar magnets 16/17 for further tuning the direction of the ion beam 15.
However, as well-known by the one skilled in the art, all conventional control assemblies have limitations for all potential implementations on a workpiece to cover the beam optics requirements to transportion beam at various beam current from light to heavy mass species and for ion energy from several tens keV down to as low as few hundred eV. Therefore, there is a need existed to propose a novel apparatus for adjusting an ion beam, after the ion beam is exited from the mass analyzer and before the workpiece on the substrate holder.